Accordingly, the development of electronic industry is extremely fast; in particularly, the 3C electronic products (i.e., computer, communicating product, and consuming electronic device, etc.) are much more outstanding; the convenience in living brought by them makes the modern people unable to live without using 3C products and, aiming to the different needs required by different consumers, the market mechanism also develops many products with different functions, prices, and volumes, such that the consumers may have more selections; for example, a desktop PC is commonly used in home or working occasion for the usage of data management, drawing, and internet, etc; a notebook PC is often used when the user is out of home and is unable to carry a heavy desktop PC, but the user also has to bear the drawbacks of a notebook PC: its price is higher than that of a desktop PC, the sustaining power of battery is insufficient, and the problem of its uneasy upgrade for operation and apparatus, etc; furthermore, someone still complains that the notebook PC is too heavy to carry, so there is a birth of personal digital assistant (abbreviated as PDA), of which the structure is simplified from that of a computer, and which applies a simpler operation system (such as, those two groups of Palm and Win CE), such that a user may use the simple functions of internet, document management, recording personal data, etc. and, accordingly, its volume and weight are easy to carry (e.g., it can be carried in the pocket of upper clothes), and its price is also cheap, such that it is a favorite for specific hi-tech group, and its popularity in market is so obvious that everybody can be observed; therefore, the invention is a further improvement for the structure of a PDA, such that the invention may achieve the object of a more humanly convenient usage.
Please refer to FIG. 1A and FIG. 1B, which show a keystroke structure 12 that is applicable in a personal digital assistant (PDA) or other handheld electronic devices to control a cursor movement in a displaying screen and an “enter” command thereof. The keystroke structure 12 has a cap 122 with a bottom flange 124. A rod 142 extends downwardly from a bottom of the cap 122. Four switches 144 for direction control of movement of the cursor are arranged around a periphery of the rod 142. By activating the four switches 144 by tilting the cap 122 and accordingly the rod 142 in four directions, the cursor on the screen can move in four directions (i.e., upward, downward, leftward and rightward directions.) A further switch 146 for “enter” control is arranged under the rod 142 and, by vertically depressing the cap 122 and accordingly the rod 142, the switch 146 is activated to obtain an “enter” command whereby a soft key on the screen pointed by the cursor is activated. The keystroke structure 12 is arranged on a circuit board 148 in a shell 10 of the electronic device. A switch assembly 14 accommodating the five switches 144 and 146 is mounted on the circuit board 148. A hole 13 is defined in the shell 10. An upper part of the cap 122 extends upwardly through the hole 13 to facilitate the operation of the keystroke structure 12. The cap 122 and flange 124 of the conventional keystroke structure 12 are integrally formed by plastic injection molding of hard plastic material, such as ABS (Acrylonitrile-Butadiene-Styrene) resin. When the profile (thickness) of the electronic device is lowered so that a stroke of the keystroke structure 12 is reduced, the conventional keystroke structure 12 faces a problem that when the keystroke structure 12 is titled in order to move the cursor in a selected direction, the flange 124 abuts against the shell 10 before the related switch 144 for direction control is activated. Further depressing the cap 122 causes not only the related switch 144 for direction control but also the switch 146 for “enter” control to be activated; thus, the keystroke structure 12 causes the cursor on the screen to have an incorrect action.